NOVA follows geologists and microbiologists as they explore caves in various stages of
formation to investigate the role microbes play in the creation
of some limestone caves.

The program:

reviews the traditional theory that caves form when weak carbonic acid—created when flowing rain and groundwater pick up carbon dioxide from the air and soil—penetrates cracks in rocks and dissolves the limestone.

introduces the theory that microbial processes are responsible for the production of sulfuric acid that forms some caves.

examines how researchers studying caves in New Mexico's Guadalupe Mountains came to theorize that microbes feeding on oil far beneath the caves produced hydrogen sulfide gas that seeped into the rock above, mixed with oxygen in the groundwater, and formed limestone-dissolving sulfuric acid.

reviews other environments in which microbes live in extreme heat, pressure, and darkness.

presents the discovery of microbes in caves that survive solely on chemical nutrients, including a type that eats hydrogen sulfide gas and excretes sulfuric acid.